Inter-vehicle control apparatus

ABSTRACT

In an inter-vehicle control apparatus, a controller performs acceleration control of an own vehicle, based on an actual inter-vehicle physical quantity and a target inter-vehicle physical quantity. A limiter sets a limit value for a target jerk during the acceleration control. A detector detects an occurrence of at least one of: an event in which the inter-vehicle distance becomes discontinuously shorter; and an event in which a target inter-vehicle distance corresponding to the target inter-vehicle physical quantity becomes discontinuously longer. A determiner determines a risk of collision with the preceding vehicle, based on an operation state of the preceding vehicle in relation to the own vehicle. When at least one of the events is detected, the limiter sets the limit value to a value based on the risk of collision such that change in deceleration of the own vehicle is kept lower as the risk of collision decreases.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority fromJapanese Patent Application No. 2013-263938, filed Dec. 20, 2013, thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

1. Technical Field

The present invention relates to an inter-vehicle control apparatus.

2. Related Art

An inter-vehicle control apparatus that controls an inter-vehicledistance between an own vehicle and a preceding vehicle is known inrelated art (for example, refer to JP-A-2000-108720). For example, theinter-vehicle control apparatus detects the inter-vehicle distancebetween an own vehicle and a preceding vehicle using a radar apparatus.Based on the detected inter-vehicle distance, the inter-vehicle controlapparatus then performs acceleration control of the vehicle so that theinter-vehicle distance becomes closer to a target inter-vehicledistance. In another example, the inter-vehicle control apparatuscontrols the inter-vehicle distance by performing acceleration controlof the vehicle so that an inter-vehicle time, which is derived bydividing the detected inter-vehicle distance by the speed of the ownvehicle, becomes closer to a target inter-vehicle time.

In the above-described related art, the driver may perform an overrideoperation, thereby approaching the preceding vehicle. An actualinter-vehicle physical quantity corresponding to the detectedinter-vehicle distance or inter-vehicle time may become smaller than atarget inter-vehicle physical quantity corresponding to the targetinter-vehicle distance or inter-vehicle time.

In this instance, the target inter-vehicle physical quantity is changedso as to become closer to the actual inter-vehicle physical quantity,and then is gradually increased over time, thereby controlling thedegree of deceleration of the vehicle. The target inter-vehicle physicalquantity is changed to become closer to the target inter-vehiclephysical quantity that should actually be realized, as the relativespeed between the own vehicle and the preceding vehicle decreases. Thetarget inter-vehicle physical quantity is changed to become closer tothe actual inter-vehicle physical quantity, as the relative speedbetween the own vehicle and the preceding vehicle increases.

In the related art, the degree of deceleration is suppressed asdescribed above, and then, driving experience is improved. The followingcan be considered as instances in which the actual inter-vehiclephysical quantity becomes smaller than the target inter-vehicle physicalquantity. For example, a new preceding vehicle cuts in ahead of the ownvehicle. Alternatively, the target inter-vehicle physical quantity ischanged to a large value as a result of change in operating mode.

In the above-mentioned related art, the degree of deceleration issuppressed by the target inter-vehicle physical quantity being changed.For example, when a new preceding vehicle cuts in ahead of the ownvehicle and the inter-vehicle distance discontinuously changes, anunnecessarily large degree of deceleration may occur. The following canbe given as an example of when an unnecessarily large degree ofdeceleration occurs. For example, an excessively large amount ofdeceleration, which is disproportionate to the risk of collision withthe preceding vehicle felt by the driver, may occur, thereby causing thedriver some discomfort. In this way, the above-mentioned related art hasroom for improvement regarding the driving feeling.

SUMMARY

It is thus desired to provide an inter-vehicle control apparatus that iscapable of actualizing deceleration behavior of a vehicle that issuitable for feeling of a driver.

An exemplary embodiment of the present disclosure provides aninter-vehicle control apparatus that is mounted to a vehicle andincludes control means, limiting means, detecting means, and determiningmeans.

The control means performs acceleration control of an own vehicle basedon an actual inter-vehicle physical quantity and a target inter-vehiclephysical quantity. The target inter-vehicle quantity is a target valueof the actual inter-vehicle physical quantity. The actual inter-vehiclephysical quantity is a detected value of a physical quantitycorresponding to an inter-vehicle distance between the own vehicle and apreceding vehicle.

The limiting means sets a limit value for a target jerk during theacceleration control by the control means. The detecting means detectsan occurrence of at least one of: (i) an event (first event) in whichthe inter-vehicle distance becomes discontinuously shorter; and (ii) anevent (second event) in which a target inter-vehicle distancecorresponding to the target inter-vehicle physical quantity becomesdiscontinuously longer. An example of the first event may include anevent in which a new preceding vehicle cuts in ahead of the own vehicle.An example of the second event may include an event in which the targetinter-vehicle distance is changed to a value that is higher than thecurrent value as a result of change in operating mode of the vehicle.

The determining means determines the risk of collision with thepreceding vehicle felt by the driver of the own vehicle. For example,the determining means determines a risk of collision, based on theoperation state of the preceding vehicle in relation to the own vehicle.In addition, the determining means may be configured to determine therisk of collision based on a relative speed between the precedingvehicle and the own vehicle.

When the detecting means detects the above-described events, thelimiting means sets the limit value of the target jerk to a value basedon the risk of collision determined by the determining means. As aresult, the change in deceleration of the own vehicle can be kept loweras the determined risk of collision decreases.

In the inter-vehicle control apparatus of the exemplary embodiment, thetarget jerk is provided with a limit value, as described above. Thus,even when a new preceding vehicle cuts in ahead of the own vehicle andthe actual inter-vehicle physical quantity discontinuously changes,sudden deceleration caused by a discrepancy between the actualinter-vehicle physical quantity and the target inter-vehicle physicalquantity can be suppressed.

In addition, in the inter-vehicle control apparatus, based on the riskof collision with the preceding vehicle felt by the driver, the changein deceleration is kept lower as the risk of collision decreases. Whenthe driver feels a high risk of collision, the required suddendeceleration of the own vehicle is generated. When the driver does notfeel a high risk of collision, poor driving feeling due to suddendeceleration is suppressed. Therefore, in the inter-vehicle controlapparatus, preferable vehicle deceleration behavior that is suitable forfeeling of the driver can be actualized.

When the at least one of the first event and the second event isdetected, the limiting means may set, as the limit value of the targetjerk, the upper limit value of a target deceleration gradient such that:(i) the upper limit value gradually increases from an initial value, and(ii) a slope of the upper limit value is kept lower as the risk ofcollision determined by the determining means decreases.

As a result of the inter-vehicle control apparatus being configured inthis way, sudden deceleration caused by the occurrence of theabove-described events at an early stage of the events can besuppressed. In addition, the actual inter-vehicle physical quantity canbe changed to the target inter-vehicle physical quantity at a speedbased on the risk of collision felt by the driver.

Furthermore, when the at least one of the first event and the secondevent is detected, the limiting means may set the upper limit value ofthe deceleration gradient such that: (i) the upper limit value graduallyincreases from an initial value to a standard value over time; and (ii)an amount of time until the upper limit value of the decelerationgradient changes from the initial value to the standard value becomeslonger as the risk of collision decreases. As a result of a techniquefor changing the limit value of the target jerk in this way, the limitvalue can be appropriately adjusted by a simple process. Decelerationbehavior preferable to the feeling of the driver can be actualized.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram of a configuration of an on-board systemaccording to an embodiment;

FIG. 2 is a block diagram of functions actualized by a control apparatusof the on-board system shown in FIG. 1;

FIG. 3 is a flowchart of a process actualized by a correcting unitincluded in the functions of the control apparatus shown in FIG. 2;

FIG. 4 is a diagram for explaining a relationship between an actualinter-vehicle distance and a target inter-vehicle distance before andafter a target inter-vehicle distance is changed;

FIG. 5 is a diagram for explaining a correspondence between a drivingstate of a preceding vehicle and a risk of collision;

FIG. 6 is a graph of limit values of target jerk and a trajectory oftarget acceleration; and

FIG. 7 is a graph of the correspondence between a risk of collision anda relaxation time.

DESCRIPTION OF EMBODIMENTS

An example of the present invention will hereinafter be described withreference to the drawings.

An on-board system 1 of the present example is shown in FIG. 1. Theon-board system 1 is mounted to a vehicle, such as a two-wheel orfour-wheel automobile. The on-board system 1 is configured to controlthe inter-vehicle distance between an own vehicle 3 and a precedingvehicle 5 by controlling the engine and the brake. The on-board system 1mainly includes an object detection apparatus 10, a vehicle speed sensor20, an input interface 30, a control apparatus 40, an engine electroniccontrol unit (ECU) 50, and a brake ECU 60. The apparatuses composing theon-board system 1 are connected to one another via an in-vehiclenetwork. Alternatively, the apparatuses are directly connected to thecontrol apparatus 40 via dedicated cables.

The object detection apparatus 10 provides a function as a so-calledradar apparatus. The object detection apparatus 10 emits explorationwaves (such as optical waves or electromagnetic waves) ahead of the ownvehicle 3, and then receives reflection waves of the exploration waves,thereby detecting an object ahead. The object detection apparatus 10detects the distance from the own vehicle 3 to the object ahead, theorientation of the object ahead in relation to the own vehicle 3, andthe relative speed of the object ahead in relation to the own vehicle 3.

The object detection apparatus 10 may be configured to further include acamera that captures images of the area ahead of the own vehicle 3. Inthis instance, the object detection apparatus 10 may be configured todetect an object ahead based on the images captured by the camera. Theobject detection apparatus 10 may then determine the type of object. Theobject detection apparatus 10 may also determine the attitude of theobject in relation to the cruising lane of the own vehicle 3.

The object detection apparatus 10 detects the preceding vehicle 5 basedon the detection results described above. The preceding vehicle 5 is avehicle that is traveling ahead of the own vehicle 3, in the same laneas the own vehicle 3. The object detection apparatus 10 identifies adistance (in other words, the inter-vehicle distance) D and a relativespeed W of the preceding vehicle 5 in relation to the own vehicle 3. Theobject detection apparatus 10 inputs the information on theinter-vehicle distance D and the relative speed W to the controlapparatus 40.

Meanwhile, the vehicle speed sensor 20 detects the vehicle speed V ofthe own vehicle 3. The vehicle speed sensor 20 then inputs the speedinformation to the control apparatus 40. In addition, the inputinterface 30 inputs operation information on operations performed by thedriver to the control apparatus 40. The input interface 30 includes, asswitches that are operable by the driver, a switch for inputting anexecution command for an inter-vehicle control process and a switch forswitching operating modes.

The control apparatus 40 starts the inter-vehicle control process whenthe execution command is inputted from the input interface 30. In theinter-vehicle control process, the control apparatus 40 controls theinter-vehicle distance D to a target inter-vehicle distance Dr based onthe information on the inter-vehicle distance D and the relative speed Winputted from the object detection apparatus 10, and the vehicle speed Vof the own vehicle 3 inputted from the vehicle speed sensor 20.

The control apparatus 40 includes a central processing unit (CPU) 41, aread-only memory (ROM) 43, and a random access memory (RAM) 45. The ROM43 stores therein various programs. The RAM 45 is used as a work areawhen the CPU 41 performs processes. The control apparatus 40 actualizesvarious functions required for inter-vehicle control by the CPU 41performing various processes based on the above-described programs. Whenperforming the inter-vehicle control process, the control apparatus 40inputs, to the engine ECU 50 or the brake ECU 60, a drive command or abrake command to control the acceleration A of the own vehicle.

In the present specification, “acceleration” in the direction in whichthe own vehicle 3 accelerates ahead is set to a positive value.Conversely, “acceleration” in the direction of deceleration is set to anegative value. “Deceleration” in the present specification refers to avalue obtained by inverting the sign (positive/negative) of the“acceleration”. The “relative speed” of the preceding vehicle 5 inrelation to the own vehicle 3 is set to a positive value when the speedof the preceding vehicle 5 is higher than the speed of the own vehicle3. The “relative speed” is set to a negative value when the speed of thepreceding vehicle 5 is lower than the speed of the own vehicle 3.

The engine ECU 50 controls the engine so that the wheels generate adriving torque that is based on the above-described drive command fromthe control apparatus 40. The brake ECU 60 controls the hydraulic brakeso that the wheels generate a braking torque that is based on the brakecommand from the control apparatus 40.

Next, a detailed configuration of the control apparatus 40 will bedescribed. As a result of the CPU 41 performing various processes basedon the programs, the control apparatus 40 functions as a targetinter-vehicle distance setting unit 401, a target jerk setting unit 403,a correcting unit 405, a target acceleration setting unit 407, and anacceleration control unit 409, as shown in FIG. 2. However, the controlapparatus 40 may be configured as a dedicated circuit that includes acircuit group for functioning as these units.

The target inter-vehicle distance setting unit 401 sets the targetinter-vehicle distance Dr between the own vehicle 3 and the precedingvehicle 5. Specifically, the target inter-vehicle distance setting unit401 sets the target inter-vehicle distance Dr corresponding to theoperating mode selected by the driver, based on a command from thedriver that is inputted via the input interface 30. The operating modesinclude short distance mode and long distance mode.

When short distance mode is selected as the operating mode, the targetinter-vehicle distance setting unit 401 sets, as the targetinter-vehicle distance Dr, a target inter-vehicle distance Dr1 for shortdistance mode. The target inter-vehicle distance Dr1 for short distancemode is set in advance. On the other hand, when long distance mode isselected as the operating mode, the target inter-vehicle distancesetting unit 401 sets a target inter-vehicle distance Dr2 for longdistance mode as the target inter-vehicle distance Dr. The targetinter-vehicle distance Dr2 for long distance mode is longer than thetarget inter-vehicle distance Dr1 for short distance mode.

The target jerk setting unit 403 sets a target jerk Jr for bringing theinter-vehicle distance D closer to the target inter-vehicle distance Dr,based on the inter-vehicle distance D detected by the object detectionapparatus 10 and the target inter-vehicle distance Dr. In addition tothe inter-vehicle distance D and the target inter-vehicle distance Dr,the target jerk Jr can be set using the speed V and the acceleration Aof the own vehicle 3.

In the present specification, the actual inter-vehicle distance, jerk,acceleration, and speed are indicated, rather than the target values,when simply expressed as inter-vehicle distance, jerk, acceleration, andspeed. The acceleration A of the own vehicle 3 can be determined by atime derivative of the speed V detected by the vehicle speed sensor 20.The jerk Jr can be determined by a time derivative of the accelerationA.

A following technique is already known. In this known technique, thetarget acceleration Ar or the target jerk Jr are set to bring theinter-vehicle distance D closer to the target inter-vehicle distance Dr.The inter-vehicle distance D is controlled to the target inter-vehicledistance Dr based on the target acceleration Ar or the target jerk Jr.The target jerk setting unit 403 can set the target jerk Jr based onthis known technique.

The correcting unit 405 corrects the target jerk Jr set by the targetjerk setting unit 403. The correcting unit 405 then inputs the correctedtarget jerk Jc to the target acceleration setting unit 407.Specifically, when the target jerk Jr inputted from the target jerksetting unit 403 is less than a target jerk limit value (referred to,hereinafter, as simply a “limit value”) JL that is set to a negativevalue (Jr<JL), the correcting unit 405 corrects the target jerk Jr tothe limit value JL. The correcting unit 405 then inputs the correctedtarget jerk Jc=JL to the target acceleration setting unit 407.

On the other hand, when the target jerk Jr inputted from the target jerksetting unit 403 is the limit value JL or higher(Jr≧JL), the correctingunit 405 does not correct the target jerk Jr. The correcting unit 405sets the corrected target jerk Jc to the same value as the target jerkJr. The correcting unit 405 then inputs the corrected target jerk Jc=Jrto the target acceleration setting unit 407. The sign-inverted value(−JL) of the limit value JL corresponds to an upper limit value of atarget deceleration gradient (time derivative of a target deceleration).

In the on-board system 1 of the present example, when the target jerk Jcis a negative value, the deceleration of the own vehicle 3 increasedmore quickly, as the target jerk Jc decreases (as the absolute valueincreases).

Based on the corrected target jerk Jc corrected by the correcting unit405, the target acceleration setting unit 407 sets the targetacceleration Ar corresponding to the target jerk Jc. Based on theacceleration A of the own vehicle 3 and the target acceleration Ar setby the target acceleration setting unit 407, the acceleration controlunit 409 calculates the required drive torque or brake torque to bringthe acceleration A of the own vehicle 3 closer to the targetacceleration A. The acceleration control unit 409 then inputs, to theengine ECU 50 or the brake ECU 60, a drive command or a brake command toactualize the drive torque or the brake torque. As a result, theacceleration control unit 409 controls the acceleration A of the ownvehicle 3 to the target acceleration Ar.

When the process shown in FIG. 3 is started, the correcting unit 405determines whether or not a cut-in event by a preceding vehicle 5 hasoccurred (step S110). The cut-in event by a preceding vehicle 5 refersto an event in which a new preceding vehicle 5 enters the area ahead ofthe own vehicle 3.

When determined that a cut-in event by a preceding vehicle 5 hasoccurred, the point of reference for the inter-vehicle distance Dswitches from the existing preceding vehicle 5 to the new precedingvehicle 5 that has entered between the own vehicle 3 and the existingpreceding vehicle 5. The inter-vehicle distance D between the ownvehicle 3 and the preceding vehicle 5 becomes discontinuously shorter.As a result, a discrepancy occurs between the inter-vehicle distance Dand the target inter-vehicle distance Dr. The target jerk setting unit403 sets a target jerk Jr that has a high target deceleration gradientto reduce the discrepancy.

In other words, the target jerk setting unit 403 sets the target jerk Jrto a negative value that has a high absolute value. In the presentexample, the target jerk Jr is corrected by a special method in asituation such as this. Therefore, the above-described determination ismade. The determination regarding whether or not the cut-in event hasoccurred can be actualized by the object detection apparatus 10inputting information on the preceding vehicle 5 required fordetermination to the control apparatus 40.

When determined that the cut-in event has occurred (Yes at step S110),the correcting unit 405 proceeds to step S130. When determined that thecut-in event has not occurred (No at step S110), the correcting unit 405proceeds to step S120.

After proceeding to step S120, the correcting unit 405 determineswhether or not a switching event has occurred. The switching eventrefers to when the operating mode for inter-vehicle control is switchedfrom the above-described short distance mode to long distance mode. Thedetermination can be actualized by monitoring of the operationinformation from the input interface 30.

As shown in FIG. 4, as a result of the switching event, the targetinter-vehicle distance Dr is discontinuously switched from the targetinter-vehicle distance Dr=Dr1 in short distance mode to the targetinter-vehicle distance Dr=Dr2 in long distance mode. A discrepancyoccurs between the inter-vehicle distance D and the target inter-vehicledistance Dr. As a result, in a manner similar to that when the cut-inevent by the preceding vehicle 5 occurs, the target jerk setting unit403 sets the target jerk Jr that a high target deceleration gradient toreduce the discrepancy.

Therefore, when determined that the above-described switching event hasoccurred (Yes at step S120), the correcting unit 405 proceeds to stepS130. On the other hand, when determined that the switching event hasnot occurred (No at step S120), the correcting unit 405 proceeds to stepS180.

After proceeding to step S180, the correcting unit 405 sets the limitvalue JL of the target jerk Jr to a standard value JL0. The standardvalue JL0 is a negative value that is determined in advance by thedesigner. Thereafter, based on the limit value JL=JL0, the correctingunit 405 inputs the corrected target jerk Jc corresponding to the targetjerk Jr to the target acceleration setting unit 407 (step S190).

In other words, when determined that the target jerk Jr is less than thelimit value JL=JL0, the correcting unit 405 corrects the target jerk Jrto the limit value JL=JL0. The correcting unit 405 then inputs thecorrected target jerk Jc=JL0 to the target acceleration setting unit407. On the other hand, when determined that the target jerk Jr is thelimit value JL=JL0 or higher, the correcting unit 405 sets the correctedtarget jerk Jc to the same value as the target jerk Jr. The correctingunit 405 then inputs the corrected target jerk Jc=Jr to the targetacceleration setting unit 407. Thereafter, the correcting unit 405temporarily ends the process shown in FIG. 3.

Conversely, after proceeding to step S130, the correcting unit 405calculates a risk of collision Z. The risk of collision Z refers to therisk of collision between the own vehicle 3 and the preceding vehicle 5as felt by the driver of the own vehicle 3. Specifically, the risk ofcollision Z is calculated based on the inter-vehicle distance D betweenthe own vehicle 3 and the preceding vehicle 5, the relative speed W ofthe preceding vehicle 5 in relation to the own vehicle 3, and the speedV of the own vehicle 3. For example, the risk of collision Z iscalculated based on the following expression.

Z=α/THW+β/TTC

THW=D/N

TTC=D/(−W)

Here, α and β are positive coefficients. In the above-describedexpression, the risk of collision Z is calculated to be a higher valueas the speed V of the own vehicle 3 in relation to the inter-vehicledistance D increases. In addition, the risk of collision Z is calculatedto be a higher value as the relative speed W in relation to theinter-vehicle distance D becomes a higher value in the direction(negative direction) in which the preceding vehicle 5 nears the ownvehicle 3. The relative speed W in relation to the inter-vehicledistance D indicates the operation state of the preceding vehicle 5.However, the lower limit of the risk of collision Z is zero.

The driver tends to feel a greater risk of collision with the precedingvehicle 5 as the speed V of the vehicle 3 in relation to theinter-vehicle distance D increases. In addition, the driver tends tofeel a greater risk of collision with the preceding vehicle 5 as thetime to collision TTC with the preceding vehicle 5 become shorter.Therefore, as a result of the risk of collision Z being calculated basedon the expression above, an appropriate value can be calculated as therisk of collision felt by the driver.

The left-hand section of FIG. 5 shows an example in which theinter-vehicle distance D is shorter than the target inter-vehicledistance Dr as a result of the cut-in event by the preceding vehicle 5.In the example, the speed of the preceding vehicle 5 is 80 km per hour.The speed of the own vehicle is 60 km per hour. The right-hand sectionof FIG. 5 shows an example in which the speed of the preceding vehicle 5is 60 km per hour. The speed of the own vehicle is 60 km per hour.

When the combination of the inter-vehicle distance D and the targetinter-vehicle distance Dr is the same in both the first example shown inthe left-hand section of FIG. 5 and the second example shown in theright-hand section of FIG. 5, the risk of collision Z=Z1 in the firstexample is calculated to be a value lower than the risk of collisionZ=Z2 in the second example.

In the first example, the relative speed W is a positive value, and thepreceding vehicle 5 is moving away from the own vehicle 3. In the secondexample, the relative speed W is zero. In addition, the risk ofcollision Z=Z1 in the first example and the risk of collision Z=Z2 inthe second example are calculated to be values lower than the risk ofcollision Z when the relative speed W is a negative value and the ownvehicle 3 is nearing the preceding vehicle 5.

After completing the calculation of the risk of collision Z, such asthat described above, the correcting unit 405 sets a reduction time Txbased on the calculated risk of collision (step S140). The reductiontime Tx refers to the amount of time until the limit value JL is reducedto the standard value JL0.

As shown in the upper section of FIG. 6, in the present example, whenthe cut-in event by the preceding vehicle 5 and the switching event ofthe operating mode occur, the limit value JL is gradually changed in alinear manner from the initial value zero to the standard value JL0. Inother words, the upper limit value (−JL) of the target decelerationgradient (−Jr) is gradually changed to increase from the initial valuezero to the standard value (−JL0). The reduction time Tx corresponds tothe amount of time until the limit value JL is changed from the initialvalue zero to the standard value JL0 in this way.

The dotted line shown in the graph indicating time t in relation tolimit value JL, shown in the upper section of FIG. 6, is the trajectoryof the limit value JL when the reduction time Tx is a value Tx1. Thebroken line is the trajectory of the limit value JL when the reductiontime is a value Tx2 that is greater than the value Tx1. The solid lineis the trajectory of the limit value JL when the reduction time is avalue Tx3 that is greater than the value Tx2.

Meanwhile, the dotted line shown in the graph indicating time t inrelation to target acceleration Ar, shown in the lower section of FIG.6, is an example of the target acceleration Ar when the reduction timeTx is the value Tx1. The broken line is an example of the targetacceleration Ar when the reduction time Tx is the value Tx2. The solidline is an example of the target acceleration Ar when the reduction timeTx is the value Tx3.

As shown in FIG. 7, the reduction time Tx is set so as to be amonotonically non-increasing function or a monotonically decreasingfunction in relation to the risk of collision Z. In this relationship,the reduction time Tx is set to a higher value as the risk of collisionZ decreases. However, the correspondence between the risk of collision Zand the reduction time Tx shown in FIG. 7 is an example. Variousrelationships in which the reduction time Tx increases as the risk ofcollision Z decreases can be used.

In the present example, the reduction time Tx is set to a higher valueas the risk of collision Z decreases. Therefore, the slope of the limitvalue JL (in other words, the upper limit value of the targetdeceleration gradient) is kept lower as the risk of collision Zdecreases. The target acceleration (target deceleration) is graduallychanged. As a result, the jerk J (deceleration gradient) in the ownvehicle 3 immediately after the occurrence of the above-described eventscan be suppressed. As shown in the lower section of FIG. 6, unnecessarysudden deceleration of the own vehicle 3 can be prevented. The drivingexperience can be improved.

At step S140, the reduction time Tx based on the risk of collision Zcalculated at step S130 is set based on a function indicating thecorrespondence between the risk of collision Z and the reduction time Txthat has been set in advance. However, at step S140, the reduction timeTx based on the risk of collision Z calculated at step S130 may be setbased on a table indicating the correspondence between the risk ofcollision Z and the reduction time Tx that has been stored in advance inthe Rom 43. The function and the table can be generated based on theresults of experiments related to driving experience.

The control apparatus 40 subsequently proceeds to step S150. The controlapparatus 40 determines whether or not elapsed time t from theoccurrence of the above-described cut-in event or switching event hasexceeded the reduction time Tx. When determined that the elapsed time thas not exceeded the reduction time Tx (No at step S150), the controlapparatus 40 proceeds to step S160. As a result, the control apparatus40 repeatedly performs the processes at steps S160 and S170 until theelapsed time t exceeds the reduction time Tx.

At step S160, the control apparatus 40 calculates and sets the limitvalue JL using by following expression, based on the standard value JL0,the elapsed time t, and the reduction time Tx.

JL=(JL0/Tx)·t

At step S170, when determined that the target jerk Jr is less than thelimit value JL (Jr<JL), the correcting unit 405 corrects the target jerkJr to the limit value JL. The correcting unit 405 then inputs thecorrected target jerk Jc=JL=(JL0/Tx)·t to the target accelerationsetting unit 407. When determined that the target jerk Jr is the limitvalue JL or higher (Jr≧JL), the correcting unit 405 sets the correctedtarget jerk Jc to the same value as the target jerk Jr. The correctingunit 405 then inputs the corrected target jerk Jc=Jr to the targetacceleration setting unit 407.

In this way, when the above-described events occur, the correcting unit405 sets the limit value JL so as to gradually change from the initialvalue zero to the standard value JL0 over time. Sudden deceleration isthereby suppressed. In other words, the correcting unit 405 sets theupper limit value (=Jl) of the target deceleration gradient so as togradually change from the initial value zero to the standard value(−JL0). The correcting unit 405 thereby corrects the target jerk Jr soas to suppress sudden deceleration.

Then, when determined that the elapsed time t has exceeded the reductiontime Tx (Yes at step S150), the correcting unit 405 sets the limit valueJL to the standard value JL0 (step S180). The correcting unit 405corrects the target jerk Jr based on the standard value JL0 (step S190).

The on-board system 1 of the present example is as described above. Inthe on-board system 1, when the above-described events occur, the limitvalue JL based on the risk of collision Z with the preceding vehicle 5felt by the driver is set for the target jerk Jr. As a result of thelimit value JL being provided, the jerk in the own vehicle 3 can belimited regardless of the discrepancy between the inter-vehicle distanceD and the target inter-vehicle distance Dr. The occurrence of suddendeceleration that is caused by the discrepancy and is disproportionateto the risk felt by the driver can be prevented from occurring in theown vehicle 3.

In particular, in the on-board system 1, based on the risk of collisionZ with the preceding vehicle 5 felt by the driver, the change indeceleration is kept lower as the risk of collision Z decreases.Therefore, when the driver feels a high risk of collision, the requiredsudden deceleration of the own vehicle 3 is generated. When the driverdoes not feel a high risk of collision, poor driving experience due tosudden deceleration is suppressed. Therefore, in the on-board system 1,preferable vehicle deceleration behavior that is suited for feeling ofthe driver can be actualized.

In addition, in the on-board system 1, the risk of collision Z iscalculated based on the relative speed W between the preceding vehicle 5and the own vehicle 3. Therefore, the risk of collision Z felt by thedriver can be appropriately calculated. In particular, in the on-boardsystem 1, based on the actual inter-vehicle distance D, the speed V ofthe own vehicle 3, and the relative speed W, the risk of collision Z iscalculated to be a higher value as the speed V of the own vehicle 3 inrelation to the inter-vehicle distance D increases, and as the relativespeed W in relation to the inter-vehicle distance D increases in thedirection in which the preceding vehicle 5 nears the own vehicle 3.Therefore, a more appropriate value can be calculated as the risk ofcollision Z.

In addition, in the on-board system 1, when the above-described eventsdo not occur, the limit value JL is set to the standard value JL0. Whenthe events are detected, the limit value JL is set so that the upperlimit value (sign-inversed value of the limit value JL) of the targetdeceleration gradient is set to gradually increase from the initialvalue zero to the standard value over time. Furthermore, the limit valueJL is set so that the slope of the upper limit value is kept lower asthe risk of collision Z decreases.

Therefore, sudden deceleration caused by the occurrence of theabove-described events at an early stage of the events can besuppressed. In addition, the inter-vehicle distance D can be changed tothe target inter-vehicle distance Dr at a speed based on the risk ofcollision Z felt by the driver.

The present disclosure is not limited to the above-described example.Various aspects are also possible. For example, instead of theinter-vehicle distance D and the target inter-vehicle distance Dr, theinter-vehicle time (D/V) and the target inter-vehicle time (Dr/V) can beused to perform inter-vehicle control of the own vehicle 3. Here, theinter-vehicle time (D/V) and the target inter-vehicle time (Dr/V) arerespectively the inter-vehicle distance D and the target inter-vehicledistance Dr divided by the speed V of the own vehicle 3.

Moreover, in the example described above, the on-board system 1 ismounted in a vehicle that uses an internal combustion engine as a powersource. However, the present invention may be mounted in various typesof vehicles, such as a vehicle that uses an electric motor as a powersource. In addition, the present invention may be applied to an on-boardsystem that performs deceleration control only when the inter-vehicledistance is shorter than the target inter-vehicle distance, withoutperforming acceleration control when the inter-vehicle distance islonger than the target inter-vehicle distance.

In addition, the method for calculating the risk of collision Z felt bythe driver is not limited to the above-described expression. Forexample, the risk of collision Z may be calculated taking intoconsideration the surrounding road environment, the personality of thedriver, and the like, in addition to the operation state of thepreceding vehicle 5. For example, uncertainties are stronger regardingthe behavior of the preceding vehicle 5 several seconds into the futureon a local road, compared to a highway. It is considered that the driverwill more easily feel risk. Therefore, increasing the allowable targetdeceleration gradient may be considered. In addition, informationrelated to the personality of the driver may be acquired from the drivervia the input interface 30. The computational expression for the risk ofcollision Z may be changed. Alternatively, the reduction time Tx inrelation to the risk of collision Z may be changed.

Finally, correspondence will be described. The control apparatus 40corresponds to an example of the inter-vehicle control apparatus. Thetarget jerk setting unit 403, the target acceleration setting unit 407,and the acceleration control unit 409 correspond to an example ofcontrol means (equivalent to a control unit or a controller). Thefunctions actualized by steps S110 and S120 performed by the correctingunit 405 correspond to functions actualized by detecting means(equivalent to a detecting unit or a detector). The functions actualizedby step S130 correspond to functions actualized by determining means(equivalent to a determining unit or a determiner). The functionsactualized by steps S140 to S160 correspond to an example of functionsactualized by limiting means (equivalent to a limiting unit or alimiter).

What is claimed is:
 1. An inter-vehicle control apparatus mounted to anown vehicle, the inter-vehicle control apparatus comprising: controlmeans that performs acceleration control of the own vehicle based on anactual inter-vehicle physical quantity and a target inter-vehiclephysical quantity, where the actual inter-vehicle physical quantity is adetected value of a physical quantity corresponding to an inter-vehicledistance between the own vehicle and a preceding vehicle, and the targetinter-vehicle quantity is a target value of the actual inter-vehiclephysical quantity; limiting means that sets a limit value for a targetjerk during the acceleration control; detecting means that detects anoccurrence of at least one of: (i) a first event in which theinter-vehicle distance becomes discontinuously shorter; and (ii) asecond event in which a target inter-vehicle distance corresponding tothe target inter-vehicle physical quantity becomes discontinuouslylonger; and determining means that determines a risk of collision withthe preceding vehicle felt by the driver of the own vehicle, based on anoperation state of the preceding vehicle in relation to the own vehicle,when the detecting means detects the at least one of the first event andthe second event, the limiting means setting the limit value for thetarget jerk to a value based on the risk of collision determined by thedetermining means such that change in deceleration of the own vehicle iskept lower as the determined risk of collision decreases.
 2. Theinter-vehicle control apparatus according to claim 1, wherein thedetermining means determines the risk of collision, based on a relativespeed between the preceding vehicle and the own vehicle.
 3. Theinter-vehicle control apparatus according to claim 2, wherein when theat least one of the first event and the second event is detected, thelimiting means sets, as the limit value for the target jerk, an upperlimit value of a target deceleration gradient such that: (i) the upperlimit value gradually increases from an initial value; and (ii) a slopeof the upper limit value is kept lower as the risk of collisiondetermined by the determining means decreases.
 4. The inter-vehiclecontrol apparatus according to claim 3, wherein when the at least one ofthe first event and the second event is detected, the limiting meanssets the upper limit value such that: (i) the upper limit valuegradually increases from an initial value to a standard value over time;and (ii) an amount of time until the upper limit value of thedeceleration gradient changes from the initial value to the standardvalue becomes longer as the risk of collision decreases.
 5. Theinter-vehicle control apparatus according to claim 4, wherein thedetermining means determines the risk of collision based on: (i) aninter-vehicle distance between the own vehicle and the precedingvehicle; (ii) a speed of the own vehicle; and (iii) a relative speedbetween the preceding vehicle and the own vehicle.
 6. The inter-vehiclecontrol apparatus according to claim 5, wherein the determining meanscalculates the risk of collision to be a higher value, as the speed ofthe own vehicle in relation to the inter-vehicle distance increases, andas the relative speed in relation to the inter-vehicle distance becomesa larger value in a direction in which the preceding vehicle nears theown vehicle.
 7. The inter-vehicle control apparatus according to claim6, wherein the detecting means detects, as the occurrence of the firstevent in which the inter-vehicle distance becomes discontinuouslyshorter, an occurrence of an event in which a new preceding vehicleenters the area ahead of the own vehicle.
 8. The inter-vehicle controlapparatus according to claim 7, wherein the detecting means detects, asthe occurrence of the second event in which a target inter-vehicledistance corresponding to the target inter-vehicle physical quantitybecomes discontinuously longer, an occurrence of an event in which thetarget inter-vehicle distance is changed to a value larger than acurrent value, as a result of change in operating mode of the vehicle.9. The inter-vehicle control apparatus according to claim 1, whereinwhen the at least one of the first event and the second event isdetected, the limiting means sets, as the limit value for the targetjerk, an upper limit value of a target deceleration gradient such that:(i) the upper limit value gradually increases from an initial value; and(ii) a slope of the upper limit value is kept lower as the risk ofcollision determined by the determining means decreases.
 10. Theinter-vehicle control apparatus according to claim 9, wherein when theat least one of the first event and the second event is detected, thelimiting means sets the upper limit value such that: (i) the upper limitvalue gradually increases from an initial value to a standard value overtime; and (ii) an amount of time until the upper limit value of thedeceleration gradient changes from the initial value to the standardvalue becomes longer as the risk of collision decreases.
 11. Theinter-vehicle control apparatus according to claim 1, wherein thedetermining means determines the risk of collision based on: (i) aninter-vehicle distance between the own vehicle and the precedingvehicle; (ii) a speed of the own vehicle; and (iii) a relative speedbetween the preceding vehicle and the own vehicle.
 12. The inter-vehiclecontrol apparatus according to claim 11, wherein the determining meanscalculates the risk of collision to be a higher value, as the speed ofthe own vehicle in relation to the inter-vehicle distance increases, andas the relative speed in relation to the inter-vehicle distance becomesa larger value in a direction in which the preceding vehicle nears theown vehicle.
 13. The inter-vehicle control apparatus according to claim1, wherein the detecting means detects, as the occurrence of the firstevent in which the inter-vehicle distance becomes discontinuouslyshorter, an occurrence of an event in which a new preceding vehicleenters the area ahead of the own vehicle.
 14. The inter-vehicle controlapparatus according to claim 1, wherein the detecting means detects, asthe occurrence of the second event in which a target inter-vehicledistance corresponding to the target inter-vehicle physical quantitybecomes discontinuously longer, an occurrence of an event in which thetarget inter-vehicle distance is changed to a value larger than acurrent value, as a result of change in operating mode of the vehicle.15. An inter-vehicle control method comprising: performing, by controlmeans of an inter-vehicle control apparatus mounted to an own vehicle,acceleration control of the own vehicle based on an actual inter-vehiclephysical quantity and a target inter-vehicle physical quantity, wherethe actual inter-vehicle physical quantity is a detected value of aphysical quantity corresponding to an inter-vehicle distance between theown vehicle and a preceding vehicle, and the target inter-vehiclequantity is a target value of the actual inter-vehicle physicalquantity; setting, by limiting means of the inter-vehicle controlapparatus, a limit value for a target jerk during the accelerationcontrol; detecting, by detecting means of the inter-vehicle controlapparatus, an occurrence of at least one of: (i) a first event in whichthe inter-vehicle distance becomes discontinuously shorter; and (ii) asecond event in which a target inter-vehicle distance corresponding tothe target inter-vehicle physical quantity becomes discontinuouslylonger; determining, by determining means of the inter-vehicle controlapparatus, a risk of collision with the preceding vehicle felt by thedriver of the own vehicle, based on an operation state of the precedingvehicle in relation to the own vehicle; and when the detecting meansdetects the at least one of the first event and the second event,setting, by the limiting means, the limit value of the target jerk to avalue based on the determined risk of collision such that change indeceleration of the own vehicle is kept lower as the determined risk ofcollision decreases.